1. Field of the Invention
This invention relates generally to the field of semiconductor fabrication. More specifically, the invention relates to compositions and methods for semiconductor film deposition of Ta or Nb doped high-k materials.
2. Background of the Invention
With the dramatic shrinkage in new semiconductor based-devices, one of the most concerning issues of scaling metal-oxide-semiconductor field effect transistors (MOSFETs) is the increase of gate leakage current by direct tunneling because the thickness of silicon dioxide (SiO2) gate insulators cannot be reduced further than about 1 nm. Silicon dioxide has been used as a gate oxide material for decades. As transistors have decreased in size, the thickness of the silicon dioxide gate dielectric has steadily decreased to increase the gate capacitance and thereby drive current and device performance. As the thickness scales below 2 nm, leakage currents due to tunneling increase drastically, leading to unwieldy power consumption and reduced device reliability. Replacing the silicon dioxide gate dielectric with a high dielectric constant (high-k) material allows increased gate capacitance without the concomitant leakage effects.
Hafnium silicate and hafnium silicon oxynitride have been regarded as some of the most promising high-k materials to replace silicon dioxide. The inclusion of silicon and nitrogen theoretically prevents the formation and the diffusion of SiO gas at the high-k/substrate interface. The most popular alternative to hafnium silicate and hafnium silicon oxynitride has been HfAlOx films.
Another approach is to form HfTaOx films by alternative pulses (ALD mode) of a Hf precursor, H2O (or another O source), a Ta precursor, H2O again these pulses being separated by an appropriate purge by an inert gas (this sequence forms one cycle which will be typically repeated several thousand times). As a result, the substrate surface is OH terminated after each H2O pulse and the Hf or Ta precursors, if suitable, react with the surface in the following pulse. Nevertheless, tantalum suffers because of its very limited volatility. The most popular tantalum alkoxide, polyethylene terephthalate (PET) Ta(OEt)5 is volatile only above 130° C. However, for thin film deposition vaporization temperatures higher than 150° C. are generally required. The lack of volatility of these compounds is mainly due to the dimer structure of the molecule. Using higher alkoxides will not lead to a significantly more volatile molecule as an additional carbon atom on each of the ligand would increase the molecular weight. As such, there are no known solutions to adequately deposit HfTaO or HfFaON with chemical precursors using current deposition techniques such as chemical vapor deposition (CVD), pulsed CVD or atomic layer deposition (ALD).
Consequently, there is a need for methods and compositions for deposition of metal-TaO and/or metal-TaON for semiconductor fabrication.